Conventional processes for treating crude oil involve distillation, and then various cracking, solvent refining, and hydroconversion processes, so as to produce a desired group of products, such as fuels, lubricating oil products, petro-chemicals, chemical feedstocks, and the like. An exemplary process includes the distillation of the crude oil in an appropriate atmospheric distillation column, resulting in gas oil, naphtha, other gases, and atmospheric residuum. This last portion is fractionated further in a vacuum distillation column, so as to produce so-called vacuum gas oil, and vacuum residuum. The vacuum gas oil, in turn, is usually cracked via fluid catalytic cracking or hydrocracking, to produce more valuable light transportation fuel products, while the residuum can be processed further, to yield additional useful products. The methods involved in these processes can include, e.g., hydrotreating or fluid catalytic cracking of the residuum, coking, and solvent deasphalting. Any materials recovered from crude distillation at fuel boiling points have typically been used, directly, as fuels.
To elaborate on the processes described, supra, solvent deasphalting is a physical, separation process, where feed components are recovered in their original states, i.e., they do not undergo chemical reactions. Generally, a paraffinic solvent, containing 3-7 or 8 carbon molecules, is used to separate the components of the heavy crude oil fractions. It is a flexible process, which essentially separates atmospheric, and vacuum heavy residues, typically into two products: (i) asphalt and (ii) deasphalted or demetallized oil, referred to as “DAO” or “DMO,” respectively hereafter. The choice of solvent is left to the skilled artisan, and is chosen with desired products, yields, and quantities in mind, as are other process parameters, such as the operating temperature, operating pressure, and the solvent/oil ratio. As a general rule, as the molecular weight of the solvent increases, so does solubility of the oil into the solvent. For example, either propane or a propane/isobutane mixture is typically used to manufacture lube oil bright stock. If, on the other hand, the DAO will be used in conversion practices, like fluid catalytic cracking, solvents with higher molecular weights (e.g., butane or pentane, or mixtures thereof), are used. The products of DAO solvation include those described supra, as well as lube hydrocracking feed, fuels, hydrocracker feed, fluid catalytic cracking feed, and fuel oil blends. The asphalt product may be used as a blending component for various grades of asphalt, as a fuel oil blending component, or as a feedstock for heavy oil conversion units (e.g., cokers.)
Conventional solvent deasphalting methods are carried out without catalysts or adsorbents. U.S. Pat. No. 7,566,394, the disclosure of which is incorporated by reference, teaches improved solvent deasphalting methods which employ solid adsorbents. The improvement in the methodology leads to separation of nitrogen and polynuclear aromatics from DAO. The adsorbents are then removed with the asphalt products, and are either sent to an asphalt pool, or gasified in a membrane wall gasifier, where solids are required.
Hydrocracking processes, as is well known, are used commercially in many refineries. A typical application of a hydrocracking process involves processing feedstreams which boil at 370° C. to 565° C. in conventional units, and those which boil at 520° C. and above, in so-called “residue units.” Simply stated, hydrocracking is a process by which C—C bonds of large molecules in a feedstream, are broken, to form smaller molecules, which have higher volatility and economic value. In addition, hydrocracking processes typically improve the quality of hydrocarbon feedstock, by increasing the H/C ratio via hydrogenation of aromatic compounds, and by removing organo-sulfur, and organic nitrogen compounds.
Given the significant economic benefits that result from hydrocracking, it is not surprising that there have been substantial developments in improving hydrocracking processes, and the development of more active catalysts.
In practice, hydrocracking units usually include two principal zones: a reaction zone and a separation zone. There are also three standard configurations: single stage, series-flow (“once-through”), with and without recycling, and two stage processes, with recycling. The choice of reaction zone configuration depends upon various parameters, such as feedstock quality, the product specification and processing objectives, and catalyst selection.
Single stage, once-through hydrocracking processes are carried out at operating conditions which are more severe than typical hydrotreating processes, but which are less severe than conventional full pressure hydrocracking processes. Mild hydrocracking is more cost effective than more severe processes but, generally, it results in production of lesser amounts of desired middle distillate products, which are of lower quality than the products of conventional hydrocracking.
Single or multiple catalyst systems can be used depending upon, e.g., the feedstock processed and product specifications. Single stage hydrocracking units are generally the simplest configuration, designed to maximize middle distillate yield over a single or dual catalyst system. Dual catalyst systems are used in stacked-bed configurations or in two different reactors.
Feedstock is typically refined over one or more amorphous-based hydrotreating catalysts, either in the first catalytic zone in a single reactor, or in the first reactor of a two-reactor system. The effluents of the first stage are then passed to the second catalyst system which consists of an amorphous-based catalyst or zeolite catalyst having hydrogenation and/or hydrocracking functions, either in the bottom of a single reactor or the second reactor of a two-reactor system.
In two-stage configurations, which can also be operated in a “recycle-to-extinction” mode of operation, the feedstock is refined by passing it over a hydrotreating catalyst bed in the first reactor. The effluents, together with the second stage effluents, are passed to a fractionator column to separate the H2S, NH3, light gases (C1-C4), naphtha and diesel products which boil at a temperature range of 36-370° C. The unconverted bottoms, free of H2S, NH3, etc. are sent to the second stage for complete conversion. The hydrocarbons boiling above 370° C. are then recycled to the first stage reactor or the second stage reactor.
Hydrocracking unit effluents are sent to a distillation column to fractionate the naphtha, jet fuel/kerosene, diesel, and unconverted products which boil in the nominal ranges of 36-180° C., 180-240° C., 240-370° C. and above 370° C., respectively. The hydrocracked jet fuel/kerosene products (i.e., smoke point >25 mm) and diesel products (i.e., cetane number >52) are of high quality and well above worldwide transportation fuel specifications. While hydrocracking unit effluents generally have low aromaticity, any aromatics that remain will lower the key indicative properties of smoke point and cetane numbers for these products.
One major technical challenge posed in hydrotreating and/or hydrocracking heavy oil fractions or whole crude is the effect of small concentrations of contaminants, such as organic nickel or vanadium containing compounds, as well as poly nuclear aromatic compounds. These organometallic compounds, and others, reduce the activity or lifetime of hydrotreating catalysts. The contaminants and polynuclear aromatics cause reduced process performance, a need for increased capital, and higher operating costs for refinery processing units. The metals in the residual fraction of the crude oil deposit on the hydroprocessing catalyst pores and results in catalyst deactivation. These problems are addressed and solved in the disclosure which follows.
Conventional, prior art processes in the field of the invention involve distillation of crude oil, followed by treatment of the light fractions (naptha and diesel fuel) which remain following distillation. These light fractions are desulfurized and/or treated (i.e., “reforming” in the case of naphtha) to improve their quality, and are then sent to fuel pools for further use. The vacuum residium, referred to supra, is treated via solvent deasphalting, so as to secure deasphalted oil and asphalt. Asphalt is then further treated, by being gasified, or it is sent to the “asphalt pool.”
Prior art processes show the treatment of fractionates or distillates of crude oil, rather than treatment of crude oil per se, as in accordance with the invention. See, e.g., PCT/EP2008/005210 where distillates are used to produce asphaltenes and DAO; U.S. Pat. No. 3,902,991, wherein a vacuum residuum is solvent extracted followed by hydrocracking and gasification of the DAO and asphalt; published U.S. Patent Application 2011/0198266, showing treatment of a vacuum residue; published U.S. Patent Application 2008/0223754, where residues from a distillation process are used to manufacture asphaltene and DAO; and EP 683 218, which also teaches treating residual hydrocarbon products. Also see, e.g., U.S. Pat. Nos. 8,110,090; 7,347,051; 6,357,526; 6,241,874; 5,958,365; 5,384,297; 4,938,682; 4,039,429; and 2,940,920, as well as Published U.S. Patent Application 2006/0272983; PCT/KR2010/007651, European Patent Application 99 141; and Published Japanese Patent Application 8-231965. All references discussed herein are incorporated by reference in their entirety.
The current invention simplifies and improves the prior art process, by eliminating the need for distillation, and for treating the naptha and diesel fractions. Rather, the invention, as will be seen, simplifies whole crude oil processing by hydrocracking the whole stream, and eliminating the steps referred to supra, while providing a method for delayed coking of fractions produced by the method.
How the invention is achieved will be seen in the disclosure which follows.